The HD 8901 is a portable instrument with interchangeable probes for measuring absolute and relative humidity, dew point and temperature. The humidity sensor is a condenser the dielectric of which is a hygroscopic polymer. As the dielectric constant for water is around 80, a strong variation of capacity is obtained with the variation of the humidity content of this polymer. The particular advantages of this type of sensor are good linearity, insensitivity to temperature variations, brief response time and long life. The temperature is measured by a Pt100 platinum thermoresistance (the temperature working range is limited by the working range of the humidity sensor). The sensor is flat, with a high surface/volume ratio; this allows a good response time. The HD 8901 is easy to use.


Measures:
Relative humidity
Absolute humidity
Dew point temperature
Temperature in °C and °F
Relative values
Maximum and minimum values
The heart of the instrument is a microprocessor.
The functions of the instrument are:
- AUTO-POWER-OFF: the instrument switches of automatically after about 8 minutes.
- Relative measurements.
- REC: stores the maximum and minimum value of the two inputs in all functions.
- HOLD: blocks the reading on the display, while internally the instrument continues to update the values.
- A beep sounds to indicate that a key has been activated; a beep every 30 seconds indicates that the battery is running low; also, the symbol appears on the display.